Changes In Corticosteroid-binding Globulin Research Articles

New Roles for Corticosteroid Binding Globulin and Opposite Expression Profiles in Lung and Liver.

Corticosteroid-binding globulin (CBG) is the specific plasma transport glycoprotein for glucocorticoids. Circulating CBG is mainly synthesized in liver but, its synthesis has been located also in other organs as placenta, kidney and adipose tissue with unknown role. Using an experimental model of acute pancreatitis in cbg-/- mice we investigated whether changes in CBG affect the progression of the disease as well as the metabolism of glucocorticoids in the lung. Lack of CBG does not modify the progression of inflammation associated to pancreatitis but resulted in the loss of gender differences in corticosterone serum levels. In the lung, CBG expression and protein level were detected, and it is noteworthy that these showed a sexual dimorphism opposite to the liver, i.e. with higher levels in males. Reduced expression of 11β-HSD2, the enzyme involved in the deactivation of corticosterone, was also observed. Our results indicate that, in addition to glucocorticoids transporter, CBG is involved in the gender differences observed in corticosteroids circulating levels and plays a role in the local regulation of corticosteroids availability in organs like lung.

Using changes in binding globulins to assess oral contraceptive pill compliance

Measuring ethinyl estradiol (EE2) induced changes in binding globulin (BG) levels may provide an effective and convenient approach to distinguishing noncompliant from compliant oral contraceptive pill (OCP) users in research settings. This analysis evaluated the validity of using changes in corticosteroid-binding globulin (CBG), sex-hormone-binding globulin (SHBG), thyroxine-binding globulin (TBG), as measures of OCP compliance.

Corticosteroid-binding globulin reactive centre loop antibodies recognise only the intact natured protein: Elastase cleaved and uncleaved CBG may coexist in circulation

Corticosteroid-binding globulin (CBG) is the principal carrier of cortisol in circulation and is a non-inhibitory member of the serpin family of serine proteinase inhibitors. It possesses an exposed elastase specific site which, when cleaved, allows a conformational change promoting the delivery of cortisol to sites of inflammation. Previously there was no ability to independently distinguish between the uncleaved, stressed, conformer of CBG and total CBG in circulation. Here we raised and characterized monoclonal antibodies generated against a synthetic peptide spanning the elastase cleavage site within the exposed reactive centre loop (RCL) and measured changes in CBG by ELISA following treatment with human neutrophil elastase. The antibodies recognized the synthetic peptide as well as intact CBG and the epitope (STGVTLNL) spanned the elastase cleavage site. Treatment of plasma with elastase resulted in a complete loss of CBG levels determined using these RCL antibodies whereas CBG levels measured with an unrelated CBG monoclonal antibody were unaffected. We also compared plasma levels of CBG measured by RCL antibodies and an unrelated CBG antibody and showed discordance in some samples. This study shows for the first time the ability to measure the intact, stressed conformer of CBG. We report discordance with total CBG in some samples implying the presence of cleaved CBG in circulation. This is an important finding as it has implications for free cortisol which hitherto have been determined from total cortisol and total CBG levels. This antibody could be used for determining the time course of intact CBG in various relevant patient cohorts and for structure/function studies on the biology of human CBG.

How acute is the acute stress response? Baseline corticosterone and corticosteroid-binding globulin levels change 24 h after an acute stressor in Japanese quail

Changes in plasma corticosteroid-binding globulin (CBG) capacity can alter free plasma concentration and tissue availability of glucocorticoids (GC) and hence alter the organismal response to stress. However, CBG change in response to stress has not been extensively studied. While it is clear that chronic stress can causes CBG decline and in some species acute stressors can reduce CBG during the 30–60 min of the stressor, more long-term changes in CBG following an acute stressor has received less attention. Here we investigated corticosterone (CORT: the primary GC in birds) and CBG levels 24 h after an acute stressor in a unique study system: Japanese quail divergently selected for CORT reactivity to acute stress. Using this model, we examined the interaction of selected CORT reactivity with CBG response to determine if CBG shows a delayed decline in response to an acute stressor and if that decline varies by selected genetic background. We found lowered CBG capacity, elevated total CORT and free CORT 24 h after acute stress in all three quail groups. These results demonstrate for the first time in an avian species that exposure to an acute stressor can affect CBG and CORT 24 h later.

Impact of live trapping on stress profiles of Richardson’s ground squirrel ( Spermophilus richardsonii)

Researching the physiological ecology of natural populations requires an understanding of the impact of capture-induced stress because of its numerous effects on physiological processes. In many cases, initial blood samples to which comparisons are made are obtained well after capture and may differ markedly from free-ranging conditions. We examined the extent to which stress profiles of male Richardson’s ground squirrels ( Spermophilus richardsonii) were affected by short-term responses to live trapping. We compared stress profiles of true base animals (blood samples obtained <3 min of capture) with those of nominal base animals (blood samples obtained >1 h after capture). Total cortisol increased almost 40% whereas our measure of corticosteroid binding globulin (CBG) decreased by 21%, resulting in a two-fold increase in free cortisol levels in nominal base animals compared with true base animals. Capture caused androgen concentrations to fall to almost half of those of true base animals. Energy mobilization increased markedly (22% in glucose and 221% in free fatty acids). Although white blood cell counts did not change, the number of neutrophils was 48% higher in true base animals. There were no changes in hematocrit or lymphocyte counts. Although most of the changes were predictable, the changes in CBG and androgens were unexpected based on previous work on closely related Arctic ground squirrels ( Spermophilus parryii). Our results emphasize the value of obtaining true base measurements whenever possible in order to assess the directions and degree of bias introduced by trapping.

Characterization and quantification of corticosteroid-binding globulin in a southern toad, Bufo terrestris, exposed to coal-combustion-waste

Corticosteroid-binding globulin (CBG) is a plasma protein that binds corticosterone and may regulate access of hormone to tissues. The role of CBG during a stress response is not clear. At least two hypotheses have been proposed: 1) CBG levels may increase in response to a stressor, thereby decreasing the amount of circulating free corticosterone, or 2) CBG levels may decline, making corticosterone available for its role in increased metabolic needs during stress. In this study, southern toads, Bufo terrestris, were exposed to a chronic pollutant (coal-combustion-waste), to determine changes in CBG and free corticosterone levels. Since toads exposed to chronic pollutants in previous studies did not exhibit the predicted changes in metabolic rate and mass, but did experience a significant elevation in total corticosterone, we hypothesized that CBG would likewise increase and thus, mitigate the effects of a chronic (i.e. 2 months) pollutant stressor. To conduct this study, we first characterized the properties of CBG in southern toads. Toad CBG has a K d = 20.6 ± 1.0 nM and a B max = 332.2 ± 5.1 nmol/L plasma. The rank order potencies for steroid inhibition of tritiated corticosterone are: dihydrotestosterone > corticosterone ≫ progesterone = testosterone ⋙ estrogen = dexamethasone. After characterization, we monitored the changes in CBG, total corticosterone, and free corticosterone in male toads that were exposed to either coal-combustion-waste or control conditions. CBG increased in all groups throughout the experiment. Total corticosterone, on the other hand, was only significantly elevated at four weeks of exposure to coal-combustion-waste. The increase in CBG did not parallel the increase in total corticosterone; as a result, free corticosterone levels were not buffered by CBG, but showed a peak at four weeks similar to total corticosterone. This finding indicates that, in this species, CBG may not provide a protective mechanism during long-term pollution exposure.

Corticosteroid and immune responses to cardiac surgery

Serum corticosteroid-binding globulin (CBG) and cortisol levels as well as subsets of circulating immunocompetent cells (ICCs) were measured during cardiac surgery. Closed heart surgery (closed mitral commissurotomy) resulted in an elevation of cortisol levels (up to 32 ± 5 μg/dL by the end of the surgery) with no changes in CBG and ICC levels observed. Open heart surgery (open reconstruction of the mitral valve) in surface-induced hypothermia (without extracorporeal bypass) caused a dramatic drop in CBG activity (from 250 ± 17 μM before the beginning of anesthesia to 198 ± 15 μM by the end of cooling (just before cardiac arrest) and 158 ± 13 μM after 30 min of reperfusion), whereas cortisol levels were only slightly elevated by the end of cooling, and a significant increase (up to 17 ± 2 μg/dL) was observed only at the end of the surgery (60 min of reperfusion and warming). Similar to CBG, a significant decline in circulating ICC contents occurred in response to cooling and circulatory arrest.

In vivo effect of free fatty acids on the specific binding of glucocorticosteroids to corticosteroid binding globulin and liver receptors in immature rats

Stimulating lipase activity with heparin (200 IU/kg b.w.) increased the plasma free fatty acid (FFA) concentration of immature rats (15 days). The effect of this elevated FFA concentration on glucocorticoid binding to corticosteroid binding globulin (CBG), and liver cytosol glucocorticoid receptor (GR), was analyzed. The plasma FFA concentration increased 2-fold, 10 minutes ( P < 0.001), 20 minutes ( P < 0.01), and 60 minutes ( P < 0.01) post-heparin. The corticosterone (B) and progesterone concentrations were unchanged 60 minutes post-injection. The binding activity of immature rat CBG for B dropped 50% ( P < 0.001) 60 minutes post-heparin injection, decreased B binding and increased plasma FFA were correlated ( r = −0.8 ). The decreased B binding resulted from a 2-fold decrease in the apparent number of CBG binding sites; the affinity constant (K a) remained unchanged. The liver cytosol endogenous FFA content of immature rats was also increased 2-fold, 60 minutes after heparin-induced lipolysis. The increased cytosol FFA, with no significant change in glucocorticoid, was accompanied by a significant decrease in dexamethasone binding to liver cytosol glucocorticoid receptor. The decrease resulted from a significantly lower apparent K a for dexamethasone and fewer receptor binding sites (n). There was a good inverse correlation between K a ( r = −0.93 ) and n ( r = −0.90 ) and the increased liver cytosol FFA content. Thus the higher plasma FFA induced in vivo by lipase activation or a standard FFA mixture probably causes conformational changes in CBG and GR, reducing glucocorticoid binding to immature rat CBG and liver GR.

The effect of acute and chronic ACTH administration on pituitary-adrenal response to acute immobilization stress. Relationship to changes in corticosteroid-binding globulin.

The effect of single and chronic ACTH administration on serum levels of the corticosteroid-binding globulin (CBG) and pituitary-adrenal (PA) responsiveness to acute immobilization (IMO) stress was studied in adult Sprague-Dawley rats. Single ACTH administration significantly reduced CBG levels but did not alter PA response to acute IMO. Chronic ACTH administration caused a greater fall in CBG than single ACTH administration and blunted PA response to IMO. The effect of chronic ACTH administration on CGB levels recovered 2 days after the last administration, but the ACTH response to IMO was normal only by day 7 after the last ACTH injection. The present data indicate that ACTH administration to rats reduced CBG levels and impaired PA response to acute stress, but impaired PA responsiveness cannot be solely attributed to changes in CBG.

Stimulation of the binding properties of adult rat corticosteroid- binding globulin by a lipolysis-induced rise in plasma free fatty acids

In vitro studies have shown that FFA induce conformational changes in human corticosteroid-binding globulin (CBG). We increased the plasma FFA concentrations of adult male rats by injecting heparin to determine whether such changes in CBG binding and immunological properties also occur in vivo. The in vivo transient activation of lipase by heparin produced a large increase in plasma FFA at 10 and 20 min (P < 0.01), which was maximal at 60 min (P < 0.005) and remained elevated at 120 min (P < 0.01) postinjection. This rise in FFA was associated with a 2- to 3-fold increase in the binding indices (C values; liters per g) of corticosterone (B) and progesterone to CBG 60-120 min postinjection (P < 0.001). There was a good positive correlation (r = 0.85) between the increase in B binding and the rise in plasma FFA in heparin-treated rats. The enhanced B binding to CBG resulted from a 2-fold increase in the apparent number of binding sites, without any significant change in the affinity constant (Ka). FFA extracted from postheparin plasma and a standard FFA mixture induced similar changes in B binding to purified mature rat CBG. The immunological behavior of CBG was not significantly changed after heparin-induced lipolysis, but the immunoreactivity of CBG from heparin-treated rats was more reduced by incubation with exogenous FFA than that from controls. FFA extracted from the plasma of heparin-treated rats and a standard FFA mixture both produced a dose-dependent drop in the immunodetection of pure CBG. These binding and immunological studies indicate that FFA mediate conformational changes in rat CBG in vivo. Thus, FFA, in addition to their roles as metabolic energy sources and components of complex lipids, can be rapid potent endogenous modulators of steroid-protein interactions.

Stimulation of the binding properties of adult rat corticosteroid-binding globulin by a lipolysis-induced rise in plasma free fatty acids.

In vitro studies have shown that FFA induce conformational changes in human corticosteroid-binding globulin (CBG). We increased the plasma FFA concentrations of adult male rats by injecting heparin to determine whether such changes in CBG binding and immunological properties also occur in vivo. The in vivo transient activation of lipase by heparin produced a large increase in plasma FFA at 10 and 20 min (P < 0.01), which was maximal at 60 min (P < 0.005) and remained elevated at 120 min (P < 0.01) postinjection. This rise in FFA was associated with a 2- to 3-fold increase in the binding indices (C values; liters per g) of corticosterone (B) and progesterone to CBG 60-120 min postinjection (P < 0.001). There was a good positive correlation (r = 0.85) between the increase in B binding and the rise in plasma FFA in heparin-treated rats. The enhanced B binding to CBG resulted from a 2-fold increase in the apparent number of binding sites, without any significant change in the affinity constant (Ka). FFA extracted from postheparin plasma and a standard FFA mixture induced similar changes in B binding to purified mature rat CBG. The immunological behavior of CBG was not significantly changed after heparin-induced lipolysis, but the immunoreactivity of CBG from heparin-treated rats was more reduced by incubation with exogenous FFA than that from controls. FFA extracted from the plasma of heparin-treated rats and a standard FFA mixture both produced a dose-dependent drop in the immunodetection of pure CBG. These binding and immunological studies indicate that FFA mediate conformational changes in rat CBG in vivo. Thus, FFA, in addition to their roles as metabolic energy sources and components of complex lipids, can be rapid potent endogenous modulators of steroid-protein interactions.

Ontogeny and regulation of corticosteroid binding globulin capacity in plasma of fetal and newborn lambs.

The developmental pattern for plasma corticosteroid binding globulin (CBG) and unbound corticoids was studied in fetal and newborn sheep. CBG capacity in the fetus increased progressively from a value of 1.6 micrograms cortisol bound/dl plasma at 75 days gestation to 7.1 micrograms/dl at 141 days (n = 249), with a greater rate of increase after 120 days. By contrast total plasma proteins increased by about 50% during the third trimester. There was an accelerated increase in the concentration of both CBG and total proteins with labor, apparently reflecting hemoconcentration. The rate of increase in total plasma corticoids was similar to that for CBG capacity; however, corticoids began their major rise later in gestation (approximately 130 days). The concentration of unbound corticoids was 0.09 micrograms/dl at 115 days and did not increase until after 135 days, reaching a maximal level of 1.87 micrograms/dl on the day before spontaneous term delivery. After birth, CBG capacity decreased from a prepartum value of 11.4 micrograms/dl to 0.6 micrograms/dl at 14 days of age, whereas total plasma proteins were constant. Total and free corticoid levels also decreased postnatally, but at a slower rate than for CBG. The expected rise in fetal CBG capacity during the third trimester did not occur in hydranencephalic, stalk-sectioned, and hypophysectomized fetuses with loss of pituitary function. Under the conditions used, there was no precocious increase in CBG concentrations with infusion of hydrocortisone, PRL, or 17 beta-estradiol to intact fetuses, and infusion of ACTH to a hypophysectomized fetus did not affect the level of CBG. Thus, there is a marked increase in CBG capacity prenatally and a rapid decrease after birth. These changes in CBG may be responsible, at least in part, for the similar changes in total corticoid concentrations. We conclude that pituitary hormone(s) regulate CBG in the sheep fetus and speculate that this effect involves the placenta.

Progesterone and corticosteroids in the initiation of lactation in the sow.

The concentration of lactose in the mammary secretion from individual glands of two sows increased significantly (P less than 0.01) between 0 and 24 h after parturition. In six sows studied during the perinatal period there was a negative correlation (r = -0.80; P less than 0.02) at parturition between the concentration of progesterone in the blood and the concentration of lactose in the mammary secretion. Furthermore, the increase in concentration of lactose in the mammary secretion after parturition was related to the timing of the decline of plasma progesterone to low levels. The results indicate that the initiation of lactation occurs within 24 h of parturition in most sows, and the results are consistent with the hypothesis that progesterone withdrawal acts as the 'trigger'. Neither the changes in corticosteroid binding globulin nor the changes in total corticosteroids were temporally related to the initiation of lactation. However, a circadian rhythm was observed for total corticosteroids in the blood of three out of nine lactating and pregnant sows, whereas no circadian rhythm was observed in progesterone of the four pregnant sows. The results are discussed in relation to the disease complex mastitis-metritis-agalactia.

Relationship between the pituitary gland and the corticosteroid-binding globulin in the rat.

Changes in corticosteroidbinding globulin (CBG) activity of rat serum were measured by multiple equilibrium dialysis at 37 C. Adrenalectomy in male and female rats increased, and in adrenalectomized animals the administration of corticosterone or cortisol decreased CBG activity; cortisol was 5 times more potent than corticosterone. The increase in CBG activity after adrenalectomy was not observed in animals which were both adrenalectomized and hypophysectomized. The injection of estradiol into intact male rats resulted in a 43% increase in CBG activity over noninjected controls; similar injections into either hypophysectomized or hypophysectomized- adrenalectomized animals did not alter the binding activity. An increase in the ACTH level by either unilateral adrenalectomy or by injection of ACTH into hypophysectomized- adrenalectomized animals did not affect the CBG activity. The results suggest that the pituitary gland is necessary for the increase in CBG activity observed after adrenalectomy or after es...